1. Field of the Invention
This invention relates generally to beverage warmers like electrical hot plates more particularly to beverage warmers used to maintain beverages within a serving carafe at a preselected elevated temperature.
2. Discussion of the Prior Art
Transparent glass carafes for use with electrical coffee or tea brewers or hot water dispensers are well known. Often the brewer has an underlying hot plate upon which the carafe is supported both during a brew cycle and afterwards. Such hot plates are generally heated by an electrical resistive heating coil. After completion of a brew cycle, carafes filled with freshly brewed beverage are also often moved to a serving location spaced from the coffee maker and kept warm on a separate, free standing, electrical hot plate similar to that associated with the beverage brewer.
Although the glass is relatively fragile compared to other materials, it is commonly used because of its transparency allowing remote, visual determination of contents without the need for electronic level indicators or the like. The glass of such carafe is tempered to withstand the heat without deleterious effects. Clear plastics that are tougher than glass are not used to make such carafes because of their relatively low fusion, melting or deterioration temperatures.
A problem with using such electrically heated hot plates heated by electrical, resistive heating coils is that the heating plates are maintained at a temperature that is hot to the touch and can cause burn injury to human flesh. If the carafe is removed from the hot plate, the hot plate remains hot. In addition, in the case of boiling water with such a hot plate the glass, itself, must become as hot as, or hotter than, the boiling temperature and is thus also hot and potentially dangerous to users. In addition, the power efficiency of heating with electrical resistive heating elements is relatively low due to the loss of heat into the air from the hot plate when the carafe is removed and the heated carafe, itself.
It is known to use relatively higher efficiency induction heaters for food preparation on cooking ranges and the like, but again the food containers must be heated to a temperature above the desired interior temperature of the food in order to cook the food and is thus often maintained at elevated hot temperatures that are dangerous to touch.
In some warmers, the induction heating element is placed inside the beverage container but these other know units also suffer from some disadvantages with respect to selectively changing the degree of heating and prevention of overheating.
Accordingly, the inventor has determined that there is a need to solve some of the safety, efficiency and other problems of known hot water heaters or hot water or beverage warmers and the like.